1. The problem asks for the coefficient of the variable in the expression $5z + \left(9 \div 3\right)$. 2. The expression consists of two parts: a variable term $5z$ and a constant term $9 \div 3$. 3. The coefficient of a variable is the numerical factor multiplying the variable. Here, the variable is $z$. 4. In the term $5z$, the coefficient is $5$ because $5$ multiplies $z$. 5. The other part $9 \div 3$ is a constant and does not affect the coefficient of $z$. 6. Therefore, the coefficient of $z$ in the expression is $5$.